With Grouping Mode set to "Bookend" or "Announce", VoiceOver can get stuck in a group. This is most easily seen in Safari: open a webpage and navigate it for a minute. Try to go to the start or end and use vo-arrows to leave the HTML Content or explore the rest of the Safari window. When you do, you become stuck in the webpage--VO simply loops around, instead of leaving. This has also happened with a Youtube video frame inside a webpage, or the HTML area of message history in Messages.